1. Field of the Invention
The present invention relates to a video switcher and a video switching method for selecting one video from a plurality of videos supplied from a plurality of video input units so as to output the selected video to a video display unit, and particularly reduce distortion of a displayed video at the time of switching videos.
2. Description of the Related Art
In video switchers which switch videos from a plurality of video input units (video sources) and simultaneously output the videos to video display units, displayed videos are distorted at the time of switching video sources. The distortion of the displayed videos is caused by discontinuity of synchronization signals from the video sources. The discontinuity of the synchronization signals occurs when the respective video sources operate independently and they are switched. A frame synchronizer is present as a device for dissolving the discontinuity of the synchronization signals, but since it is very expensive, the initial cost for the system rises drastically.
Many propositions regarding the reduction of the distortion of displayed videos at the time of switching video sources has been made. For example, there is proposed a method for setting video signals to be switched to a black level until the synchronization becomes stable and preventing distortion of the synchronization from being observed (for example, see Japanese Patent Application Laid-Open (JP-A) No. 6-149181). Also there is proposed a method for separating horizontal/vertical synchronization signals from video signals and outputting only synchronization signals for a constant time period of switching time so as to repress distortion of displayed videos at the time of switching (for example, see JP-A 6-133234).
According to the proposal of JP-A 6-149181, however, a unit for setting video signals to be switched to a black level is necessary, and thus the constitution of the switcher becomes complicated and thus the cost rises. The proposal of JP-A 6-133234, on the other hand, does not solve the discontinuity at the time of switching the synchronization signals separated from the video signals before and after switching.